doc: add return values in crypto documentation

Clarify return values for crypto.publicEncrypt and similar functions

PR-URL: https://github.com/nodejs/node/pull/16229
Fixes: https://github.com/nodejs/node/issues/12946
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Joyee Cheung <joyeec9h3@gmail.com>
Reviewed-By: Gireesh Punathil <gpunathi@in.ibm.com>

doc/api/crypto.md

@@ -1687,6 +1687,7 @@ added: v0.11.14
     `crypto.constants`, which may be: `crypto.constants.RSA_NO_PADDING`,
     `RSA_PKCS1_PADDING`, or `crypto.constants.RSA_PKCS1_OAEP_PADDING`.
 - `buffer` {Buffer | TypedArray | DataView}
+- Returns: {Buffer} A new `Buffer` with the decrypted content.
 
 Decrypts `buffer` with `privateKey`.
 
@@ -1704,6 +1705,7 @@ added: v1.1.0
     `crypto.constants`, which may be: `crypto.constants.RSA_NO_PADDING` or
     `RSA_PKCS1_PADDING`.
 - `buffer` {Buffer | TypedArray | DataView}
+- Returns: {Buffer} A new `Buffer` with the encrypted content.
 
 Encrypts `buffer` with `privateKey`.
 
@@ -1721,6 +1723,7 @@ added: v1.1.0
     `crypto.constants`, which may be: `crypto.constants.RSA_NO_PADDING` or
     `RSA_PKCS1_PADDING`.
 - `buffer` {Buffer | TypedArray | DataView}
+- Returns: {Buffer} A new `Buffer` with the decrypted content.
 
 Decrypts `buffer` with `publicKey`.
 
@@ -1741,6 +1744,7 @@ added: v0.11.14
     `crypto.constants`, which may be: `crypto.constants.RSA_NO_PADDING`,
     `RSA_PKCS1_PADDING`, or `crypto.constants.RSA_PKCS1_OAEP_PADDING`.
 - `buffer` {Buffer | TypedArray | DataView}
+- Returns: {Buffer} A new `Buffer` with the encrypted content.
 
 Encrypts the content of `buffer` with `publicKey` and returns a new
 [`Buffer`][] with encrypted content.